Magnetic random access memory (MRAM) cells using the so-called self-referenced reading operation typically comprise a magnetic tunnel junction formed of a magnetic storage layer having a magnetization which direction can be changed from a first stable direction to a second stable direction, a thin insulating layer, and a sense layer with a magnetization having a reversible direction. Self-referenced MRAM cells allows for performing the write and read operation with low power consumption and an increased speed. The self-referenced reading operation is described in European patent application EP 2276034 by the same applicant. It typically comprises as double sampling wherein the direction of sense layer magnetization is aligned in a first and second directions and the respective resistance of the magnetic tunnel junction is measured for each direction.
Self-referenced MRAM cells can be advantageously used in MRAM-based CAM, non-volatile cells for security applications including user privilege, security or encryption information on a packet-by-packet basis for high-performance data switches, firewalls, bridges, and routers. Self-referenced MRAM cells are also useful for making functional memories with a reduced yield as well as for high temperature applications.
In the case of high temperature applications, a current pulse is passed through the magnetic tunnel junction in order to heat the MRAM cell to the high temperature. This current pulse is liable to subject the thin insulating layer to a considerable electric stress. The voltage applied through the magnetic tunnel junction could possibly reach or even exceed the breakdown voltage of such insulating layer. Even if the voltage applied across the insulating layer is lower than its breakdown voltage, the stress linked to the electric current pulse can result in considerable ageing effects in the long term, notably after a great number of voltage cycles, for example during writing cycles.